Provide link to submit corrections to text through git pull requests on each page

Our documentation could be updated more often, and if we make it easier for people to contribute to it we may receive more contributions, corrections, updates.

For easy reviewing of the changes I think it would be good to provide a link to 'edit' the page, and create a pull request.

This will make users create easily reviewable pull requests, and will help get reviews from non-technical stakeholders of our team more efficiently and, I dare to say, in a more empowering way.

For example, at the end of https://support.torproject.org/tormobile/tormobile-1/ a link that says 'submit a correction' and points to https://gitlab.torproject.org/web/support/edit/master/content/tormobile/tormobile-1/contents.lr or https://github.com/torproject/support/edit/master/content/tormobile/tormobile-1/contents.lr if we want to rely on github infrastructure.